This invention relates to synthetic compositions for use as adhesives in aqueous environments. More particularly, the invention relates to biocompatible adhesive compositions.
Adhesives functional in aqueous environments have long been desired in the art. The vast majority of adhesives known to the art bind dry surfaces more strongly than the same surfaces when wet. In addition to competing with the adhesive for surface area on which to bind, water may hydrolyze or plasticize many adhesives. Of particular interest are biocompatible adhesives that function in aqueous environments, so-called "bioadhesives" . It is contemplated that bioadhesives will have much utility in biomedical applications, particularly in the areas of tissue repair, drug delivery, surgery, and in vitro cell cultivation, as well as in other areas involving aqueous environments such as chromatography and marine applications.
The bioadhesives of the art are generally derived from the naturally occurring adhesive material found in marine animals, such as mussels, barnacles, and oysters. Most of the work has concentrated on the polyphenolic protein of the marine mussel Mytilus edulis. This bioadhesive protein is thought to be dispersed as a foam from the foot of the mussel (Waite, J. H., et al., (1985), Blochem 24:5010-5014), and subsequently cured to form a cohesive, adhesive material strong enough to attach the mussel to wet surfaces. The protein is characterized by a decapeptide unit repeated 75-85 times in the native molecule and having the following amino acid sequence (Sequence Listing ID No. 1): EQU -Ala-Lys-Pro-Ser-Tyr-Xaa.sub.1 -Xaa.sub.1 -Thr-Xaa.sub.2 -Lys
where Xaa.sub.1 is hydroxyproline and Xaa.sub.2 is 3,4-dihydroxylphenylalanine (dopa). These residues are probably incorporated into the polypeptide chain as proline and tyrosine, respectively, and modified post-translationally by enzymatic hydroxylation, with the conversion of tyrosine to dopa occurring by the action of a catechol oxidase (a `tyrosinase` enzyme) present in the byssus of the mussel (Waite, J. H., (1986) Comp Physiol B 156:491).
The protein apparently has a predominantly open conformation having little or no secondary structure, as determined by recent physical studies on the solution characteristics of the protein, (Trumbore, M. W. et al., Biophys J 55:532a (1989) and Williams, T. et al., (1989) Ach. Biochem. Biophys., 269:415-422), and by application of the Chou and
Fasman algorithms to the amino acid sequence, which predict an absence of .alpha.-helices or .beta.-sheets (Williams, supra). The high concentrations of imino groups (proline, hydroxyproline), may prevent formation of substantial secondary structure within the protein.
European patent application Serial Nos. EPO 243,818 (published Nov. 4, 1987) and EPO 244,688 (published Nov. 11, 1987) describe bioadhesives comprising naturally-occurring polyphenolic protein isolated from M. edulis. U.S. Pat. Nos. 4,808,702 (Waite, J. H., issued Feb. 28, 1989) and 4,687,740 (Waite, J. H., issued Aug. 8, 1987) describe the isolation of decapeptides from these proteins, and methods of combining the peptides to form useful bioadhesive materials. AU 8,824,972 (published Mar. 23, 1989) describes water-impermeable adhesives comprising these repeating polyphenolic decapeptide units (10-400) and a bifunctional crosslinking agent.
EPO 242,656 (published Oct. 28, 1987); Marumo et al. (1986) Biochem, Biophys, Acta 872:98-103; and Swerdloff, M. D. et al, (1989) Int. J. Peptide Protein Res. 33:313 disclose methods for de novo synthesis of the M. edulis decapeptide.
PCT international patent application WO 88/03953 (published Jun. 2, 1988) describes the isolation of the genetic sequence encoding the bioadhesive precursor protein of Mytilus edulis.
It is an object of this invention to design a bioadhesive that simplifies the amino acid sequence required for cohesion and adhesion, and which does not rely on the repeating decapeptide unit. Another object of the invention is to provide an adhesive composition whose adhesive strength can be modulated and which may therefore be useful in a broad range of biomedical applications. It is also an object of this invention to design a polypeptide chain capable of forming a specific architecture which is cohesive and around which crosslinking can be designed. These and other objects and features of the invention will be apparent from the description, figures and claims which follow.